Infrared thermometer with automatic calibration

Abstract

Infrared radiation emitted from tissue surface of body cavity is measured by an infrared sensor located within a probe which generates a signal voltage dependent on the difference in temperature between the tissue and the infrared sensor. An additional ambient sensor measures the ambient temperature of the infrared sensor. The signals of the two sensors are added. To calibrate and eliminate errors, the housing of the device is provided with a chamber shaped to receive the probe and containing a target viewed by the infrared sensor. An error signal is thus generated which is added to the signals of the two sensors when they view the body tissue. A disposable, sanitary cover for the probe is made of a truncated polyethylene member of substantially uniform thickness closed by an end window. A filter in the probe suppresses absorption bands of polyethylene to eliminate errors due to minor variations in cover thickness.

What is claimed is: 
     
       1. In combination, a probe for an infrared thermometer comprising a body, first means at one end of said body having a window at its distal end for admission of infrared radiation from tissue emitting radiation, an infrared sensor in said body emitting radiation, an infrared sensor in said body emitting a first signal responsive to the radiation entering through said window, said infrared sensor being in thermal equilibrium with said body to assume the temperature of said body, an ambient sensor in thermal contact with said infrared sensor emitting a second signal responsive to the temperature of said infrared sensor, second summing means summing the output signals of said sensors, third display means responsive to said summing means indicating the temperature of said tissue; and fourth means forming a chamber having an open first end and a closed second end, a target in said chamber adjacent said second end, said target being in thermal equilibrium with said fourth means to assume the temperature of said fourth means, whereby when said probe is inserted in said chamber it receives infrared energy of measured intensity from said target, and fifth error correcting means for adding an error signal to said second summing means to correct error in the signal from said infrared sensor. 
     
     
       2. A probe according to claim 1 which further comprises a removable disposable cover for said first means cone, said cover having an end positioned over said window, said end being of a material which transmits at certain wavelength bands and absorbs at other wavelength bands, and a filter in said body between said window and said infrared sensor which suppresses the absorption bands, whereby the signal of said infrared sensor is substantially insensitive to minor variations in thickness of said end. 
     
     
       3. A probe according to claim 2 in which said cover has a body and said end is recessed relative to said body. 
     
     
       4. A probe according to claim 2 in which one end of said body is conical and said cover is a thin-walled conical member, said one end being formed with a groove and the interior of said cover being formed with a protrusion fitting into said groove to hold said cover in place. 
     
     
       5. A probe according to claim 4 which further comprises a case, a container for replacement covers having an open end, means for detachably attaching said container to said case, and a plurality of replacement conical covers in said case nested inside each other with the largest end nearest said open end, whereby when a probe is inserted into said container, said probe engages the nearest replacement cover. 
     
     
       6. A probe according to claim 2 in which one end of said body is conical and said cover is a thin-walled conical member, the exterior of said cover being formed with shoulder forming means to provide shoulders spaced outward from the proximal end of said cover whereby said shoulders engage the proximal end of a second cover nested upon said first-mentioned cover, the interior of said first-mentioned cover being formed with a protrusion fitting into said groove to hold said cover in place. 
     
     
       7. A probe according to claim 6 in which said shoulder forming means comprises longitudinal fins. 
     
     
       8. A probe according to claim 6 in which said shoulder forming means comprises a short cylindrical section located proximally of said conical member, the diameter of said cylindrical section being greater than the external diameter of said conical member. 
     
     
       9. A probe according to claim 1 in which said error correcting means comprises a second sensor in thermal contact with said target. 
     
     
       10. A probe according to claim 1 in which said fourth means comprises a case and which further comprises a switch in said case positioned to be closed when said probe is inserted in said chamber, said switch, when closed, energizing said sensors and said target. 
     
     
       11. A probe according to claim 1 in which said fourth means comprises a case and which further comprises a switch positioned at the entrance to said chamber so as to be opened if a probe with the cover attached is inserted in said chamber, said switch, when opened, inactivating said probe. 
     
     
       12. A probe according to claim 1 which further comprises peak-hold means between said summing means and said display means to hold on said display means the highest temperature sensed by said probe. 
     
     
       13. A probe according to claim 10 which further comprises a timer energized upon closing of said switch to energize said sensors and said target only for a predetermined time.